The invention generally relates to a technique and apparatus for low power wireless communication.
In a typical computer system, a main computer unit (a desktop or laptop computer, for example) communicates with various peripheral devices, such as a printer, a keyboard, a mouse, etc. Traditionally, this communication has been made possible by various cables that connect the computer unit to the peripheral devices. However, these cables place restraints on the positions of the peripheral devices relative to the computer unit, as well as contribute to excessive clutter near the computer unit.
For purposes of eliminating the cable connections between the peripheral devices and the main computer unit, short-range wireless links may be used. As an example, communication over these wireless links may be defined by a standard, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11b standard, IEEE Std. 802.11, published in 1999, and IEEE Std. 802.11b, published as a supplement to the IEEE Std. 802.11 in 1999. As another example of another standard, communication over the wireless links may be defined by what is called the Bluetooth standard, set forth by the Bluetooth Special Interest Group (SIG) in a specification entitled, “Specification of the Bluetooth System, Volume 1: Core and Volume 2: Profiles,” version 1.1, February 2001. As an example of the implementation of one of these standards, a computer system 10 may have several wireless devices that communicate over short range microwave links. For example, a main computer unit 12 may communicate over wireless links with various peripheral devices, such as a printer 14, a keyboard 16, a mouse 18, a local area network (LAN) access point 22 and a personal digital assistant (PDA) 20. The main computer unit 12 may also communicate via wireless links with one or more other computer systems, such as a computer system 29 that is depicted in FIG. 1.
A conventional wireless device that implements the IEEE 802.11b standard may include a transceiver semiconductor package, or “chip,” to demodulate signals received from an antenna of the device and modulate signals to be transmitted from the antenna. For purposes of transmitting, this transceiver chip generates a pair of balanced, modulated carrier signals. In this context, “balanced signals” refers to a pair of signals in which a current that is associated with one of the balanced signals is equal in magnitude but one hundred eighty degrees (180°) out of phase with the current that is associated with the other balanced signal. Balanced signals are ideally symmetrical with respect to ground. Thus, due to this balanced arrangement, all of the current that is communicated from one balanced output terminal of the transceiver chip returns to the other balanced output terminal of the transceiver chip without returning through ground.
In addition to the transceiver chip, the transmitter circuitry of a conventional wireless device typically includes a single-ended amplifier to generate a signal to drive the antenna in response to the balanced signals that are provided by the transceiver chip. For purposes of interfacing the amplifier to the transceiver chip, the transmitter circuitry includes a balun that transforms the balanced signals provided by the transceiver chip into a single-ended signal that is received and amplified by the amplifier. Besides transforming the balanced signals into a single-ended signal, this circuitry also attempts to match the output impedance of the transceiver to the input impedance of the amplifier. Additional impedance matching circuitry may be used between the amplifier and the antenna for purposes of attempting to match the output impedance of the amplifier to the impedance of the antenna. Unfortunately, the input and output impedances of the amplifier are typically complex and small, a condition that presents challenges in designing the impedance matching circuitry and may cause excessive power dissipation by the transmitter circuitry.
Thus, there is a continuing need for an arrangement that addresses one or more of the problems states above.